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p1518 Trouble Code

Hey new member here. Don't blow me up for not searching the forum, I just wasn't able to find the answer I needed upon searching.

2005 Legacy GT

So here's my problem, I'm getting a recurrent p1518 trouble code- starter switch circuit low input. I keep clearing it and it keeps coming back. I am having no trouble actually starting the engine until after I clear the codes. After clearing the codes I have to turn the key to the off position for 10 seconds (this is what my access port tells me to do) then it takes about 5 seconds of holding the key in the ignition position before the engine starts. This only happens on the first start after clearing the code though, after that it has no problem starting. However, sometimes it seems dependent upon how far I push in the clutch pedal, if I push it too far it just doesn't start so I back the pedal out an inch or so and the engine starts up no problem.

On other threads people are saying that it is the wiring between the ECU and the starter switch and this seems to be the case with my car as well. Does anybody know how I go about repairing this connection so that I can get rid of this CEL for good? Or does this sound like an entirely different problem?

It's 2 years later, and I don't know if this guy solved it (I sent him a PM to ask), but I am having a very similar problem with my 2005 Subaru Legacy GT, manual transmission.

Intermittently will not crank when the key is turned. If it fails too many times in a row, then I get CEL and blinking cruise light. My AP gives code P1518 (starter switch low input).

If I back off on the clutch pedal by 1" while holding key to start position then it cranks and starts (sometimes). I was suspecting the neutral safety switch and shorted it out with a jumper - thought that fixed it (indicating a bad switch), but then it failed again to start, with the jumper in place. :-( That stumped me. Back to ground zero.

Nuetral safety switch? That's only on an auto trans.
You mean the clutch pedal switch?
If you have cruise control there are two switches on the clutch pedal.

This code is caused by low voltage in the start circuit. Somewhere along the line between the fuse box, the ignition switch, the interlock relay and the clutch switch, is a loose connection or corrosion, or combination of multiple poor connections, and the voltage is dropping substantially. Got a volt meter? Pretty easy to check voltage at the clutch switch when starting.

You have the clutch switch jumped, what is it jumped with? A paper clip may do the trick temporarily, but is a high resistance connection. High resistance= drop in voltage.

Nuetral safety switch? That's only on an auto trans.
You mean the clutch pedal switch?
If you have cruise control there are two switches on the clutch pedal.

This code is caused by low voltage in the start circuit. Somewhere along the line between the fuse box, the ignition switch, the interlock relay and the clutch switch, is a loose connection or corrosion, or combination of multiple poor connections, and the voltage is dropping substantially. Got a volt meter? Pretty easy to check voltage at the clutch switch when starting.

You have the clutch switch jumped, what is it jumped with? A paper clip may do the trick temporarily, but is a high resistance connection. High resistance= drop in voltage.

Yes, the clutch pedal switch. That's what I was calling it (actually clutch safety switch, but some guy at an auto parts store said it was called the Neutral safety switch).

Anyway, yes it has cruise control. The lower switch on the pedal is for the cruise disable, if one steps on the clutch. The upper switch is used for the starting circuit. I jumped it with some 16G wire that I crimped on a male spade connector on each end, and plugged into the upper connector, once I unplugged it from the switch.

I do have a voltmeter and can try some measurements while it's failing. Where is the interlock relay located?

Yes, the clutch pedal switch. That's what I was calling it (actually clutch safety switch, but some guy at an auto parts store said it was called the Neutral safety switch).

Clutch safety switch or clutch start switch is the correct term here.

Somewhere around here is a link where you can download the Subaru factory service manual for your year. That will be a big help for component location, and the wire diagram especially.

The starter interlock relay is in the big relay panel under the dash.

But I think the start signal goes through the clutch switch. Check voltage at the switch connector while cranking. Compare that to voltage at the battery terminals while cranking.

You might just pull the start relay out and make sure the pins are clean.

The stat signal supply wire is spliced after fuse 21. One side goes to the relay the other goes to the clutch switch. If you have low voltage at the switch, check and compare voltage at fuse 21 while cranking.
Normal voltage at the fuse, and low voltage at the switch would suggest a poor connection at the splice or damaged wire somewhere between the fuse and the switch.

Thanks Fairtax4me for the information. Will keep this in mind if I have to do further debug.

I started to have doubts about the failure when jumper was installed to bypass the clutch safety switch, so reinstalled it. Have been driving a couple days with no failures to start. I plan to leave it in place for a good couple of weeks of solid use. If there are no failures then I'll remove and reconnect what I suspect is a faulty clutch safety switch. I hope at that point to have some failures again. In that case I'll just replace the switch. Otherwise, I will do debug as you suggest.